SSR 2011 does support using USB 3.0 devices as backup destinations when used for 'hot' backups/restores done via Windows (when the operating system is running).
Symantec System Recovery (SSR) 2011 does not support USB 3.0 devices, either as backup destinations or as restore media, when used for backups/restores done via the Symantec Recovery Disk (SRD).
Please take note of the following which may have an impact when using USB 3.0 3TB drives as backup destinations:
Information about Microsoft support policy for large sector drives in Windows:
An update that improves the compatibility of Windows 7 and Windows Server 2008 R2 with Advanced Format Disks is available:
Workaround (for backups/restores via the SRD):
If a USB 3.0 device is backward-compatible, connecting it to a USB 2.0 port should enable it to work with SSR at the expected throughput of USB 2.0. This workaround is unsupported, and as always, we recommend testing any USB device before relying on it for disaster recovery.
Full (hot and cold backups/restores) support for USB 3.0 is available in SSR 2013.